In modern medicine, it is common to use one or more fixation plates for treatment of spinal disorders or for fusion of vertebrae. While early procedures using fixation plates were at the lower lumbar levels, spinal fixation plates have relatively recently found applications in the instrumentation of the cervical spine. Successful spinal instrumentation in this region is particularly difficult given the known problems of safely accessing the instrumentation site.
The upper cervical spine can be approached either anteriorly or posteriorly, depending upon the spinal disorder to be treated. Complications associated with access procedures can be devastating, such as injury to the brain stem, spinal cord, and/or vertebral arteries. In addition, a lengthy access procedure can contribute to other surgical complications, such as anesthetic-related issues or surgeon fatigue.
In addition to the normal complications associated with the mere exposure and fusion of the cervical spine, implantation of a spinal fixation plate adds to the degree of risk and complication. Most users place the fixation plate over the vertebral levels to be instrumented and use the plate as a drill guide for drilling and tapping the bone in preparation for receiving a fixation screw. Several known systems and procedures provide for a soft tissue protector in the form of an elongated sleeve which is intended to surround the drill and minimize damage to the surrounding muscle and other tissues.
There is a need for a cervical plating system which minimizes the intrusion into the patient and reduces trauma to the surrounding soft tissue. Moreover, a system is required that allows for easy access to the cervical vertebrae while providing accuracy in positioning the fixation screw.
Even as the cervical spine instrumentation techniques can be improved, so can the manner of fixation of the plate to the affected vertebral levels. For example, several known plates accept spinal screws at several locations, usually at the ends and in the middle of the plate. The screws may or may not be capable of being angled at varying degrees of fixation between the vertebra and the plate. In addition, some plating systems provide a locking screw which is threaded into the expansion head of the vertebral fixation screw to lock the screw into the plate. This procedure requires the installation of a separate locking screw for every fixation screw, thereby lengthening and complicating the procedure.